Include changelog as a page in the documentation site

Migrated issue

Reported by: jonathan1055

Related to !444 (merged)

Problem/Motivation

As discovered on #3473000: Documentation pages the rendering of the CHANGELOG.md file in a 'pages' docsite is very different from when viewed in the code repo. The docsite version is not very readable, and looks awful.

Proposed resolution

• Copy the file instead of making a symlink
• Then use sed to alter some of the markdown to make it render in a more pleasing format.